1. Field of the Invention
This invention relates to electrical connectors and, more particularly, to bi-level card edge connectors and a method of fabricating an electrical contact strip having alternating first and second types of contacts for use in a bi-level connector.
2. Prior Art
In the electrical arts it is a common practice to use a connector to mechanically and electrically couple a mother printed circuit board with a daughter printed circuit board as of the vertical edge card variety. In such a practice, there has been an evolution towards placing electrical contacts closer and closer together while maintaining a high, constant stress between the electrical contacts and the areas to be contacted. In placing the contacts closer together, as to 20 contacts per linear inch, the width of each contact must decrease. This, in turn, makes it much more difficult to keep the proper contact stress between the contact and the areas to be contacted while also assuring proper alignment between the two upon insertion of the edge card into the connector. One approach in the past was to apply a spherical dimple stamped into the contact. A further approach is disclosed in co-pending U.S patent application Ser. No. 07/146,858 filed Jan. 22, 1988 entitled "Vertical Edge Card Connectors" by Thomas G. Lytle which is assigned to the same assigned as herein and is incorporated by reference in its entirety herein.
There has also been developed a special type of connector which is known in the art as a bi-level connector; i.e.: a connector having two types of contacts that make contact with a daughter printed circuit board in two locations or at two levels. The two types of contacts are generally intermixed or alternatingly arranged in two opposing rows. The first type of contacts are arranged at a predetermined pitch, such as 100 mils, between the first type of contacts. The second type of contacts are also arranged at a predetermined pitch, such as 100 mils, between the second type of contacts such that there is a 50 mils pitch between adjacent first and second contacts.
The high density card edge connector in the past encountered a problem in regard to the amount of force that was necessary to insert the edge of the daughter printed circuit board into the connector because each contact is a spring contact and it must be at least partially moved by the card edge and because there are more contacts in the high density connectors. The bi-level connector alleviated this problem to a degree by allowing for a two step engagement of the card edge with the contacts; the first step being the displacement of the upper first type of contacts and the second step being the displacement of the lower second type of contacts. However, a problem still exists when inserting a card edge into the second rows of lower contacts because, in addition to the force required to displace the lower second type of contacts, the card edge is already making contact with the first rows of upper contacts, usually at a very high stress such as about 150,000 psi per contact. An operator when inserting the daughter printed circuit board into a connector may, in attempting to overcome the high density spring forces of the contacts, damage the circuit board or connector.
Another problem that has arisen with the bi-level connectors is the fact that, in the past, the two types of contacts were manufactured separately and thus had to be inserted into the connector housing at separate operations. This requires more time, equipment and expense than a single insertion operation.
As illustrated by a great number of prior patents as well as commercial devices, efforts are continuously being made in an attempt to improve connectors and their contacts to render them more efficient, effective and economical. None of these previous efforts, however, provides the benefits attendant with the present invention. Additionally, prior connectors and contacts do not suggest the present inventive combination of method steps and component elements arranged and configured as disclosed and claimed herein. The present invention achieves its intended purposes, objects and advantages over the prior art devices through a new, useful and unobvious combination of method steps and component elements, with the use of a negligible number of functioning parts, at a reasonable cost to manufacture, and by employing only readily available materials.
It is therefore an object of the present invention to provide an electrical contact for use in a connector adapted to be attached to a mother printed circuit board and adapted to removably receive a daughter printed circuit board of the edge card type for mechanically and electrically coupling the mother and daughter printed circuit boards, the connector being of the type formed of an electrically insulating housing with a plurality of electrically conductive contacts extending therethrough for removably receiving the daughter printed circuit board, the contacts comprising two types of contacts alternatingly arranged with the second type of contacts having a variable spring rate for varying the amount of force required to displace the second type of contacts by a daughter printed circuit board.
It is a further object of the invention to provide a method of fabricating an electrical contact strip comprising alternatingly arranged first and second types of contacts.
It is a further object of the invention to provide a method of making an electrical connector with two types of contacts alternatingly arranged on a contact strip that can be simultaneously inserted into a connector housing.
It is yet a further object of this invention to miniaturize electrical connectors and their contacts.
Still a further object of the invention is to maintain a high, constant stress between electrical contacts of connectors and the contacted electrical components.
The foregoing has outlined some of the more pertinent objects of the invention. These objects should be construed to be merely illustrative of some of the more prominent features and applications of the intended invention. Many other beneficial results can be attained by applying the disclosed invention in a different manner or modifying the invention within the scope of the disclosure or prior art. Accordingly, other objects and a fuller understanding of the invention may be had by referring to the summary of the invention and the detailed description of the preferred embodiment in addition to the scope of the invention defined by the claims taken in conjunction with the accompanying drawings.